Wavelength selective switch for multimode optical systems

ABSTRACT

In an example embodiment, a WSS may include a steering element, an optical subsystem, and a cylindrical lens. The optical subsystem may include a collimating lens and a dispersive element. The optical subsystem may be located between a fiber array and the steering element. The collimating lens may be located between the fiber array and the dispersive element. The cylindrical lens may be located between the optical subsystem and the steering element.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 62/120,592, filed Feb. 25, 2015, which is incorporatedherein by reference.

FIELD

The embodiments discussed herein are related to a wavelength selectiveswitch (WSS) for multimode optical systems.

BACKGROUND

Unless otherwise indicated herein, the materials described herein arenot prior art to the claims in the present application and are notadmitted to be prior art by inclusion in this section.

In a wavelength division multiplexing (WDM) optical communicationsystem, information is carried by multiple channels, each channel havinga unique wavelength. WDM allows transmission of data from differentsources over the same fiber optic link simultaneously, since each datasource is assigned a dedicated wavelength component, or channel. Theresult is an optical communication link with an aggregate bandwidth thatincreases with the number of wavelengths, or channels, incorporated intothe WDM signal. In this way, WDM technology maximizes the use of anavailable fiber optic infrastructure; what would normally requiremultiple optic links or fibers instead requires only one.

Some WDM networks use WSS devices to dynamically route wavelengthchannels from a source to a destination. WSS devices often rely onwavelength manipulation elements such as liquid crystal on silicon(LCOS) devices or micro-electromechanical (MEMS) mirror arrays toperform the routing.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some embodiments describedherein may be practiced.

SUMMARY

Some example embodiments described herein generally relate to a WSS formultimode optical systems.

In an example embodiment, a WSS may include a steering element, anoptical subsystem, and a cylindrical lens. The optical subsystem mayinclude a collimating lens and a dispersive element. The opticalsubsystem may be located between a fiber array and the steering element.The collimating lens may be located between the fiber array and thedispersive element. The cylindrical lens may be located between theoptical subsystem and the steering element.

In an example embodiment, a wavelength selective switch (“WSS”) mayinclude an optical subsystem, a cylindrical lens, and a steeringelement. The optical subsystem may be configured to collimate anddemultiplex an input multimode optical signal into input discretewavelength channels. The optical subsystem may be configured to receivethe input multimode optical signal from an input fiber of a fiber arraythat includes the input fiber and multiple output fibers. Thecylindrical lens may be configured to focus in one dimension the inputdiscrete wavelength channels onto a steering element. The cylindricallens may be positioned substantially one focal length of the cylindricallens from the optical subsystem and substantially one focal length ofthe cylindrical lens from the steering element. The steering element maybe configured to independently redirect the input discrete wavelengthchannels such that the redirected input discrete wavelength channelsbecome output discrete wavelength channels. The cylindrical lens may befurther configured to diverge in one dimension the output discretewavelength channels onto the optical subsystem. The optical subsystemmay be further configured to converge the output discrete wavelengthchannels onto at least one output fiber.

In an example embodiment, a method may include collimating an inputmultimplexed multimode optical signal. The method may also includedemultimplexing the input multimode optical signal into discretewavelength channels. The method may also include focusing the discretewavelength channels in one dimension such that the discrete wavelengthchannels are incident on a steering element in substantially differentlocations. The method may also include selectively redirecting thediscrete wavelength channels. The method may also include collimatingthe redirected discrete wavelength channels in one dimension. The methodmay also include converging each of the redirected discrete wavelengthchannels into at least one output fiber.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential characteristics of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

Additional features and advantages of the embodiments will be set forthin the description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the embodiments. Thefeatures and advantages of the embodiments may be realized and obtainedby means of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the embodiments willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the embodiments as setforth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent embodiments, a more particular description of the embodimentswill be rendered by reference to the appended drawings. It isappreciated that these drawings depict only typical embodiments and aretherefore not to be considered limiting of its scope. The embodimentswill be described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1a is a block diagram of an example optical system that includes aWSS directing all discrete wavelength channels to one output fiber;

FIG. 1b is a block diagram of the optical system of FIG. 1a with the WSSdirecting discrete wavelength channels to different output fibers;

FIGS. 2a-2d illustrate various views of an example WSS such as may beimplemented in the optical system of FIGS. 1a-1b ; and

FIG. 3 illustrates an isometric view of an example steering element thatmay be implemented in the WSS of FIGS. 2a-2d , all arranged inaccordance with at least one embodiment described herein.

DESCRIPTION OF EMBODIMENTS

WDM optical communication systems can be used to transmit large amountsof data through fiber cables. One advantage of WDM optical communicationsystems is the ability to simultaneously transmit numerous opticalsignals composed of multiple discrete wavelength channels (“channel”)multiplexed over the same optical fiber (“fiber”). Furthermore, a WSSallows each channel to be steered independently from an input fiber toany desired output fiber.

Fibers typically come in two primary varieties, multimode fiber (MMF)and single mode fiber (SMF). SMF has a relatively smaller diameter thanMMF and typically requires a more precise source to transmit anefficient optical signal. MMF, however, is much broader in diameter andcan use more energy efficient signal sources such as VCSEL and LED lightsources. However, a common problem associated with MMF is the inabilityto effectively steer discrete wavelength channels independently. Thepresent disclosure relates to wavelength selective switching with MMFconfigurations.

Embodiments of the present disclosure will be explained with referenceto the accompanying drawings.

FIG. 1a is a block diagram of an example optical system 110 thatincludes a WSS 100 directing all discrete wavelength channels to oneoutput fiber 107 b, arranged in accordance with at least one embodimentdescribed herein. FIG. 1b is a block diagram of the optical system 100of FIG. 1a with the WSS 100 directing discrete wavelength channels todifferent output fibers 107 a-107 d (generically “output fiber 107” or“output fibers 107”), arranged in accordance with at least oneembodiment described herein. The optical system 110 may also include oneor more WDM devices 103 a-103 e (generically “WDM device 103” or “WDMdevices 103”), an input fiber 105, a multiplexed multimode input opticalsignal denoted at 101 (hereinafter “input signal 101”), a multiplexedmultimode output optical signal denoted at 102 (hereinafter “outputsignal 102”, illustrated only in FIG. 1a ), and one or morecommunication modules 109 a-109 e (generically “module 109” or “modules109”).

One or more of the modules 109 may be configured to convert one or moreelectrical signals (e.g., from a host device) to one or more opticalsignals for transmission within the optical system 110. For example, themodule 109 e may be configured to convert one or more electrical signalsto, e.g., four (or some other number) multimode optical signals that aremultiplexed by the WDM device 103 e onto the input fiber 105 as theinput signal 101. In this example, the WDM device 103 e may include amultiplexer (MUX). The input signal 101 may include four inputwavelength channels 104 a-104 d (generically “input channel 104” or“input channels 104”) and each input channel 104 may include acorresponding one of the optical signals output by the module 109 e. Theinput channels 104 of the input signal 101 can be selectively routed bythe WSS 100 to any output fiber 107. For example, in the embodimentdepicted in FIG. 1a , the input channels 104 of the input signal 101 arerouted to the output fiber 107 b and, in the output fiber 107 b, arereferred to as output wavelength channels 106 a-106 d (generically“output channel 106” or “output channels 106”) of the output signal 102.The output signal 102 may be demultiplexed by the WDM device 103 b intofour (or some other number) multimode optical signals on separateoptical paths that are received by the module 109 b and convertedthereby to one or more electrical signals that may be provided to a hostdevice. In this example, the WDM device 103 b may include ademultiplexer (DEMUX). The multiple optical signals provided to themodule 109 b may each include a corresponding one of the output channels106.

Additionally or alternatively, the WSS 100 may be configured toindependently route any input channel 104 as a corresponding outputchannel 106 to any output fiber 107. In the example embodiment depictedin FIG. 1b , the input channel 104 a is routed to the output fiber 107 aas the output channel 106 a, the input channel 104 b is routed to theoutput fiber 107 b as the output channel 106 b, the input channel 104 cis routed to the output fiber 107 c as the output channel 106 c, and theinput channel 104 d is routed to the output fiber 107 d as the outputchannel 106 d.

In the example of FIG. 1b , each WDM device 103 a-103 d receives asingle one of the output channels 106 (as opposed to receiving multipleones of the output channels 106 in a multiplexed signal, as in FIG. 1a). Accordingly, each WDM device 103 a-103 d may pass a corresponding oneof the output channels 106 through to the corresponding module 109 a-109d without performing any demultiplexing. Accordingly, the module 109 areceives the output channel 106 a, the module 109 b receives the outputchannel 106 b, the module 109 c receives the output channel 106 c, andthe module 109 d receives the output channel 106 d. Each module 109a-109 d may convert the corresponding output channel 106 to anelectrical signal that may be provided to a corresponding host device towhich each module 109 a-109 d is communicatively coupled.

The input fiber 103 and the output fibers 107 may each be composed ofany MMF such as OM1, OM2, OM3, OM4 or any other MMF. Two commonvarieties of MMF suitable for at least some embodiments described hereininclude graded index fiber and step index fiber.

The input fiber 105 and the output fibers 107 may be substantiallyphysically identical, where the input fiber 105 may include the fibercurrently carrying the input signal 101 to the WSS 100 and the outputfiber 107 may include the fiber carrying any one or more of the outputchannels 106 to a corresponding one of the WDMs 103. As such, the inputfiber 105 may function as an output fiber 107 and any of the outputfibers 107 may function as the input fiber 105 based on the origin ofthe input signal 101 and the destination(s) of the output channels 106.Accordingly, the optical system 110 may include any number ofconfigurations and orientations of the aforementioned components. Inthese and other implementations, the input fiber 105 and the outputfibers 107 may be implemented as simplex (e.g., one-way) or duplex(e.g., two-way) optical fibers. Alternatively or additionally, one ormore of the modules 109 may each be communicatively coupled to the WSS100 by two or more optical fibers, one or more of which is a dedicatedinput fiber(s) and one or more of which is a dedicated output fiber(s).

FIGS. 2a-2d illustrate various views of an example WSS 200 such as maybe implemented in the optical system 110 of FIGS. 1a-1b , arranged inaccordance with at least one embodiment described herein. The WSS 200 ofFIGS. 2a-2d is an example embodiment of the WSS 100 of FIGS. 1a-1b .Accordingly, the WSS 200 of FIGS. 2a-2d may have the same or similarfeatures as the WSS 100 of FIGS. 1a-1b . FIG. 2a depicts an isometricview of the WSS 200. FIG. 2b depicts an overhead view of the WSS 200.FIGS. 2c-2d depict side views of the WSS 200 in which the WSS 200directs discrete wavelength channels to one output (FIG. 2c ) or todifferent outputs (FIG. 2d ).

The WSS 200 may include an optical subsystem 209; a cylindrical lens215; and a steering element 217. The WSS 200 may receive a multiplexedmultimode input optical signal denoted at 201 (hereinafter “input signal201”) from an input fiber 205 (FIGS. 2c-2d ) included in a fiber array202. The input signal 201 may include or correspond to the input signal101 of FIGS. 1a-1b . As will be described in more detail herein, theinput signal 201 (or more particularly, input wavelength channels(hereafter “input channels”) included therein) may be processed by theWSS 200 and may be output as one or more output signals 219 (FIGS. 2c-2d) to one or more output fibers included in the fiber array 202. In someembodiments, the one or more output signals 219 include a multiplexedmultimode output optical signal made up of multiple output wavelengthchannels (hereafter “output channels”) and output to a single one of theoutput fibers, as illustrated in FIG. 2c . The multiplexed multimodeoutput optical signal may include or correspond to the output signal 102of FIGS. 1a-1b . In other embodiments, the one or more output signals219 include multiple output channels output to different output fibers,as illustrated in FIG. 2 d.

The fiber array 202 may include the input fiber 205 that may include orcorrespond to the input fiber 105 of FIGS. 1a-1b , and multiple outputfibers 207 a-207 b (FIGS. 2c-2d , hereafter “output fibers 207”), thatmay include or correspond to the output fibers 107 of FIGS. 1a-1b . InFIGS. 2c-2d , two unlabeled fibers of the fiber array 202 may includeone or more additional input fibers 205 and/or one or more additionaloutput fibers 207. In the example of FIGS. 2a-2d , the fibers in thefiber array 202 (including input fiber 205, output fibers 207, and theunlabeled fibers), or more particularly fiber ends of the fibers in thefiber array 202, may be vertically spaced apart from each other, e.g.,generally in a line.

The input fiber 205 may be configured to transmit the input signal 201into the WSS 200. One or more of the output fibers 207 may be configuredto receive the one or more output signals 219. Any number of spacingconfigurations of the fiber array 202 may be possible. The input fiber205 and output fibers 207 of the fiber array 202 may be configured inany order or spaced apart at any distance. The input fiber 205 may belocated at any location sufficient for transmitting the input signal 201such that the input signal 201 may interact with the components of theWSS 200. Any output fiber 207 may be located at any position sufficientfor receiving a corresponding one of the one or more output signals 219.

For example, the embodiment depicted in FIG. 2c includes the input fiber205 in the center of the fiber array 202 with the output fibers 207a-207 b located at opposite ends of the fiber array 202, each fiber ofthe fiber array 202 being substantially equally spaced apart, with theinput signal 201 transmitted by the input fiber 205; the input signal201 passing through the center of the optical subsystem 209, passingthrough the center of the cylindrical lens 215, and falling incident onthe steering element 217; the single output signal 219 (e.g., amultiplexed multimode output optical signal made up of multiple outputchannels) reflected off the steering element 217, passing through thetop half of the cylindrical lens 215 and the optical subsystem 209, andconverging on the output fiber 207 a.

The input signal 201 may include any number of input channels 204 a-204b (FIG. 2b , hereinafter “input channels 204”). Before passing throughthe optical subsystem 209, the input channels 204 may be part of thesame input signal 201. However, the input signal 201 may be dispersed(e.g., diffracted or refracted) as separate input channels 204. Forexample, the embodiment depicted in FIGS. 2a-2d includes the opticalsubsystem 209 that may be configured to separate the input channels 204horizontally, as best seen in FIG. 2b . Thus, when viewed from the sideas shown in FIGS. 2c-2d , the channels 204 substantially appear as thesame input signal 201. However, when viewed from above as shown in FIG.2b , it can be seen that the input signal 201 is dispersed into theinput channel 204 a and the input channel 204 b. Thus, the input channel204 a and the input channel 204 b are present in all of FIGS. 2a-2d evenwhen viewing angles do not allow distinguishing therebetween.Additionally, the input signal 201 is not limited to two input channels204 and may more generally include two or more input channels 204.

The one or more output signals 219 may include multiple output channels206 a-206 b (hereafter “output channels 206”) that have beenindividually steered by the steering element 217. The output channels206 may be individually steered by virtue of the corresponding inputchannels 204 being incident on the steering element 217 at regions ofthe steering element 217 that are horizontally spaced apart from eachother, as illustrated in FIGS. 2a-2b . Each region of the steeringelement 217 may be independently controlled to reflect the correspondinginput channel 204 upward or downward, thereby steering the correspondingoutput channel 206 upward or downward. In these and otherimplementations, each output channel 206 includes a corresponding inputchannel 204 after reflection thereof by the steering element 217.

In the example of FIGS. 2a-2d , the steering element 217 is configuredto steer wavelengths substantially up and down as output channels 206.The output channels 206 generally follow vertically-displaced versionsof the optical paths followed by the input channels 204, thus whenviewed from above as in FIG. 2b , the output channels 206 appear totraverse the same paths as the input channels 204. Additionally, asdepicted in FIG. 2c , when the steering element 217 steers the outputchannels 206 upward or downward by an equal amount, the output channels206 will follow the same optical path from the optical subsystem 209 toa corresponding one of the output fibers 207 (e.g., output fiber 207 ain FIG. 2c ) as a single output signal 219 made up of multiple outputchannels 206. However, as depicted in FIG. 2d , when the steeringelement 217 steers the output channels 206 upward or downward bydifferent amounts, the output channels 206 may follow verticallydisplaced optical paths from the optical subsystem 209 to correspondingones of the optical fibers 207 as multiple optical signals 219 each madeup of a single output channel 206. For instance, in FIG. 2d , the outputchannel 206 a is steered upward and is output as one output signal 219to the output fiber 207 a, while the output channel 206 b is steereddownward and is output as another output signal 219 to the output fiber207 b. Thus, the output channel 206 a and the output channel 206 b maybe present in FIGS. 2a-2b and 2d even when viewing angles do not allowdistinguishing therebetween. The output signal 219 is not limited to twooutput channels 206 and may more generally include two or more outputchannels 206 that may be independently steered in any number ofdirections by the steering element 217.

The optical subsystem 209 may be configured to demultiplex multichannelinput signals, such as the input signal 201, sufficient to substantiallyseparate the input channels 204 that make up the input signal 201. Inthe example of FIGS. 2a-2d , the optical subsystem 209 is configured todisperse the input channels 204 of the input signal 201 horizontally;however the optical subsystem 209 may more generally be configured todisperse the input signal 201 in any direction.

Furthermore, the optical subsystem 209 may include one or more opticalcomponents that collectively perform the functions described herein. Forexample, in the illustrated embodiment, the optical subsystem 209 mayinclude a collimating lens 211 and a dispersive element 213. Thecollimating lens 211 may be configured to substantially collimate theinput signal 201. For example, the embodiment illustrated in FIGS. 2a-2ddepicts the input signal 201 diverging prior to the collimating lens 211and also depicts the input signal 201 as substantially parallel (e.g.,collimated) after passing through the collimating lens 211.

The collimating lens 211 may be further configured to focus the one ormore output signals 219 onto one or more corresponding ones of theoutput fibers 207. The collimating lens 211 may include a passiveoptical element and not determinative as to which output fiber 207 anygiven output channel 206 of the one or more output signals 219 isdirected. Rather, as will be discussed later, the specific output fiber207 may depend on the reflected angle of the output channels 206 of theoutput signal 219 from the steering element 217. For example, theembodiment depicted in FIG. 2c illustrates the output channels 206 a-206b appearing substantially as one output signal 219, as reflectedsubstantially upward, relative to the WSS 200, and being focused by thecollimating lens 211 onto the output fiber 207 a.

The collimating lens 211 may include plastic, glass, or any othermaterial suitable for collimating the input signal 201. Also, thecollimating lens 211 may include an aspheric lens, a spherical lens, aparabolic lens, or any other shape suitable for collimating the inputsignal 201. In some implementations, aberrations in the collimating lens211 may reduce a coupling efficiency of the WSS 200 and as such thecollimating lens 211 may be implemented as an aspheric lens to improvethe coupling efficiency compared to some other collimating lenses.Additionally, collimating lens 211 may be placed in a locationsufficient for the input signal 201 to be substantially collimated. Inthese and other implementations, the collimating lens 211 may be placedsubstantially one focal length of the collimating lens 211 from thefiber array 202 and substantially one focal length of the collimatinglens 211 from the steering element 217. As used herein, the term“substantially” as applied to any value includes a range defined as thevalue plus or minus 10% of the value. Thus, “substantially one focallength” includes a range of distances defined as the focal length plusor minus 10% of the focal length. Moreover, insofar as the dispersiveelement 213 may change (e.g., bend) the general propagation direction ofthe input signal 201, the distance of the steering element 217 from thecollimating lens 211 (e.g., substantially one focal length of thecollimating lens 211) may be determined as the distance along an opticalpath of the input signal 201 (and/or its input channels 204) from thecollimating lens 211 to the steering element 217.

The dispersive element 213 may be configured to disperse (e.g., diffractor refract) the collimated input signal 201 into separate input channels204 in a direction sufficient for wavelength-dependent steering by thesteering element 217. This configuration may include positioning thegrating 213 at an angle sufficient to receive and disperse the inputsignal 201 into discrete input channels 204 toward the cylindrical lens215. In some embodiments, the discrete input channels 204 may overlap inthe horizontal direction even after the dispersive element 213 untilfocused (at least in one direction, e.g., horizontally) on the steeringelement 217 by the cylindrical lens 215. In an example embodiment, thedispersive element 213 may be oriented at about 45 degrees relative to apropagation direction of the input signal 201 from the fiber array 202to the dispersive element 213. The dispersive element 213 may beoriented at other angles in other embodiments. Any direction ofdispersion (e.g., diffraction or refraction) may be possible, but thedirection may determine the orientation and configuration of the otherelements of the WSS 200. The direction of dispersion and direction ofconvergence of the cylindrical lens 215 may be substantially similar.For example, the embodiment depicted in FIG. 2b illustrates thecollimated input signal 201 being dispersed horizontally into the inputchannels 204, each of which is then horizontally converged by thecylindrical lens 215 onto the steering element 217.

The dispersive element 213 may be further configured to direct theoutput channels 206 of the one or more output signals 219 toward thefiber array 202. This configuration may include positioning the grating213 at an angle sufficient to receive the output channels 206 of the oneor more output signals 219 from the cylindrical lens 215 and direct theoutput channels 206 of the one or more output signals 219 toward thefiber array 202. For example, the embodiment depicted in FIG. 2billustrates the output channel 206 a and the output channel 206 bdirected toward the center of the fiber array 202.

The dispersive element 213 may be composed of any number of materialswith any number of patterns suitable for dispersion (e.g., diffractionor refraction) of light. For example, the dispersive element 213 mayinclude glass, plastic, or any other material suitable for dispersion oflight. These materials may include properties or etch patternsconfigured to diffract light. Such etch patterns may include linesconfigured to diffract light, with linear or non-linear line spacing. Inthese and other implementations, the dispersive element 213 may includea line grating, a pulse compression grating or any other type of gratingsufficient for separating the input signal 201 into the input channels204. Alternatively, the materials making up the dispersive element mayhave a shape or other configuration suitable to refract light. In theseand other embodiments, the dispersive element 213 may include a prism.An efficiency of the dispersive element 213 may be configured to besufficient to allow the output signal 219 to be transmitted as anoptical signal by any output fiber 207.

The cylindrical lens 215 may be configured to converge the inputchannels 204 of the input signal 201 in one dimension onto the steeringelement 217. The dimension of convergence may substantially correspondwith the dispersion of optical subsystem 209. Accordingly, if theoptical subsystem 209 (and more particularly, the dispersive element213) disperses the input channels 204 horizontally, the cylindrical lens215 may converge the input channels 204 horizontally. This configurationmay include positioning the cylindrical lens 215 in a locationsufficient for receiving the input channels 204 of the input signal 201from the optical subsystem 209 and converging in one dimension the inputchannels 204 onto the face of the steering element 217. For example,FIG. 2b illustrates the input channels 204 being converged horizontallyby the cylindrical lens 215 onto the steering element 217, whereas FIGS.2c and 2d illustrate the input channels 204 not being convergedvertically by the cylindrical lens 215. There is no limitation to thenumber of input channels 204 the cylindrical lens 215 may converge.

The cylindrical lens 215 may further be configured to collimate, in thesame dimension as convergence, multiple output channels 206 of the oneor more output signal 219 and to direct the one-dimensionally collimatedoutput channels 206 onto the optical subsystem 209. This configurationmay include positioning the cylindrical lens 215 in a locationsufficient to receive the output channels 206. For example, in theembodiment of FIGS. 2a and 2b , the cylindrical lens 215 horizontallycollimates the output channel 206 a and the output channel 206 b anddirects the horizontally-collimated output channels 206 a and 206 btoward the optical subsystem 209. There is no limitation to the numberof output channels 206 the cylindrical lens 215 may collimate anddirect.

The cylindrical lens 215 may include plastic, glass, or any othermaterial suitable for optical lenses. Also, the cylindrical lens 215 maybe configured as plano-concave, plano-convex or any other in any shapesuitable for converging the input channels 204 in one dimension onto thesteering element 217, collimating, in the same direction as convergence,the output channels 206, and directing the one-dimensionally collimatedoutput channels 206 onto (or into or towards) the optical subsystem 209.Additionally, the cylindrical lens 215 may be placed in a locationsufficient for the input channels 204 to be focused in one dimensiononto the steering element 217, for the output channels 206 to beone-dimensionally collimated, and for the one-dimensionally collimatedoutput channels 206 to be directed toward the optical subsystem 209. Inthese and other implementations, the cylindrical lens 215 may be placedsubstantially one focal length of the cylindrical lens 215 from thesteering element 217 and substantially one focal length of thecylindrical lens 215 from the optical subsystem 209.

The focal length of the cylindrical lens 215 may be selected based onthe dispersive properties of the optical subsystem 209. Alternatively,the optical subsystem 209 with certain dispersive properties may beselected based on a selected focal length of the cylindrical lens 215.Various configurations or properties (e.g. line density) of the opticalsubsystem 209 may disperse the input channels 204 of the input signal201 such that the input channels 204 substantially separate at variousdistances or angles from the optical subsystem 209. Additionally, thesedispersion distances or angles from the optical subsystem 209 may alsobe affected by the wavelengths of the input channels 204 of the inputsignal 201. The properties, configuration, position, orientation, andrelationship between/of the cylindrical lens 215 and the opticalsubsystem 209 may be selected by considering these factors, such thatthe input channels 204 of the input signal 201 may be steered by thesteering element 217. For example, in some implementations, the focallength of the cylindrical lens 215 may be selected such that thecylindrical lens 215 may focus the input channels 204 of the inputsignal 201 onto the steering element 217 in a manner in which the inputchannels 204 of the input signal 201 do not overlap at all or by much onthe face of the steering element 217.

The steering element 217 may be configured to selectively steer anynumber of incident input channels 204. A number of known devices arecapable of selective wavelength steering, such as liquid silicon oncrystal (“LCOS”) and microelectromechanical mirrors (“MEMS”). Any typeof steering device sufficient for selectively and independently steeringmultiple input channels 204 may be used as the steering element 217. Inthe embodiment of FIGS. 2a-2d , the steering device 217 includes a LCOSdevice. The steering element 217 may be configured to independentlysteer individual input channels 204 as output channels 206 to any outputfiber 207. For example, in the embodiment of FIG. 2d , the input channel204 a is reflected off the steering element 217 as the output channel206 a and is steered to the output fiber 207 a and the input channel 204b is reflected off the steering element 217 as the output channel 206 band is steered to the output fiber 207 b.

Alternatively or additionally, the steering element 217 may beconfigured to steer multiple input channels 204 as output channels 206to the same output fiber 207. For example, in the embodiment of FIG. 2c, the input channel 204 a and the input channel 204 b (both labeled as“204” in FIG. 2c due to viewing angle) are reflected off the steeringelement 217 as the output channel 206 a and the output channel 206 b(both labeled as “206” in FIG. 2c due to viewing angle) and are bothsteered to the same output fiber 207 a. The steering element 217 may beconfigured to steer any number of input channels 204 to any number ofoutput fibers 207, with any combination of output channels 206 andoutput fibers 207 possible.

Furthermore, the steering element 217 may be configured to steer theinput channels 204 as output channels 206 to any different output fiber207 at any time. Embodiments of the steering element 217 such as theLCOS allow the input channels 204 to be directed as output channels 206to different output fibers 207 by programing the LCOS to reflect theincident input channels 204 as the output channels 206 at any desiredangle, determined by the wavelength of the input channel 204. Thus, anyinput channel 204 can be steered as a reflected output channel 206 to anew output fiber 207 by changing the configuration of the steeringelement 217.

FIG. 3 illustrates an isometric view of an example steering element 317that may be implemented in the WSS 200 of FIGS. 2a-2d , arranged inaccordance with at least some embodiments described herein. The steeringelement 317 may include or correspond to the steering element 217 ofFIGS. 2a-2d . The steering element 317 may include a steering axis 340,a wavelength axis 330, and one or more incident channel images (“image”)320 a-320 b (generically “image 320” or “images 320”). The steering axis340 of FIG. 3 may be parallel to vertical or a vertical direction, whichvertical or vertical direction may be at least inferred from thediscussion of FIGS. 2a-2d . The wavelength axis 330 may be parallel tohorizontal or a horizontal direction, which horizontal or horizontaldirection may be at least inferred from the discussion of FIGS. 2a -2 d.

The images 320 may be formed by incident input wavelength channels 304a-304 b (generically “input channel 304” or “input channels 304”) thatmay have the same or similar features as the input channels 204 of FIGS.2a-2d . The steering element 317 may be configured to reflect the images320 as output wavelength channels 306 a (generically “output channel306” or “output channels 306”), which may have the same or similarfeatures as the output channels 206. In the example depicted in FIG. 3,the incident input channel 304 a is reflected as the output channel 306a at a different angle of reflection than the angle of incidence of theinput channel 304 a, as determined by the steering element 317.Similarly, the incident input channel 304 b is reflected as the outputchannel 306 b at a different angle of reflection than the angle ofincidence of the input channel 304 b, as determined by the steeringelement 317.

The images 320 may be narrower with respect to the wavelength axis 330than with respect to the steering axis 340 as a result of acorresponding cylindrical lens (e.g., the cylindrical lens 215 of FIGS.2a-2d ) converging the input channels in one dimension (e.g., in thehorizontal direction which may be parallel to the wavelength axis). Insome embodiments of the steering element 317, a narrower image 320 withrespect to the wavelength axis 330 may produce more precisely steeredoutput channels 306.

Additionally, images 320 may be configured to fall incident on the faceof the steering element 317 such that there is no substantial overlapbetween images 320 on the face of the steering element 317. For example,in FIG. 3, the image 320 a and the image 320 b are on the face of thesteering element 317 in different locations with no overlap between theimage 320 a and the image 320 b. In other embodiments, there may be someoverlap between the image 320 a and the image 320 b, such as less than2%, less than 5%, less than 10%, or less than some other percentage ofoverlap.

Returning to FIGS. 2a-2d , other variations of the WSS 200 may includeconfiguring the steering element 217 to steer at least one of the one ormore output signals 219 to the input fiber 205. Thus, the WSS 200 may beconfigured to allow the input fiber 205 and the output fiber 207 to bethe same fiber. Additionally, the output signal 219 is not limited totravel through the same optics or traverse a similar path traveled bythe input signal 201. Rather, the WSS 200 may include multiple opticalsubsystems 209 and cylindrical lenses 215. For example, one suchembodiment may include a separate mirror to redirect the one or moreoutput signals 219 to such separate components configured to direct theone or more output signals 219 on any output fiber 207. Another suchembodiment may include the steering element 217 reflecting the one ormore output signals 219 to such separate components configured to directthe one or more output signals 219 on any output fiber 207. Thus, theoutput signal 219 is not limited to travel back through the exact sameoptical components of the WSS 200 as the input signal 201. Also, theoutput fiber 207 does not have to be located within the same fiber array202 as the input fiber 205, but may be positioned independent of theinput fiber 205, the other components of the WSS 200 may be positionedsufficient to direct the one or more output signals 219 to the outputfiber 207.

Modifications can be made to the WSS 200 without changing the scope ofthe disclosure. The positions, orientations, configurations, andrelationships between the individual components of the WSS 200 may bealtered such that the coupling efficiency of the WSS 200 is reduced.While such alterations may decrease the efficiency of the WSS 200, thecoupling efficiency of the WSS 200 may still be sufficiently high tosteer the output channels 206 of the output signal 219 to the outputfibers 207.

Moreover, the components of the WSS 200 do not have to steer every inputchannel 204 of the input signal 201 or every output channel 206 of theone or more output signals 219 to an output fiber 207. Rather thecomponents of the WSS 200 may only interact with the input channel 204or the output channel 206 desired for steering. For example, an inputchannel 204 not desired for steering may be dispersed by the opticalsubsystem 209 such that the undesired input channel 204 does not passthrough the cylindrical lens 215. Any input channel 204 of the inputsignal 201 or any output channel 206 of the one or more output signals219 may interact in any manner other than described or not interact atall with the components of the WSS 200 if that input channel 204 oroutput channel 206 is not desired for steering. Thus, if the inputchannel 204 or output channel 206 is not desired for steering, thatinput channel 204 or output channel 206 may reflect, refract, diffract,converge, diverge, focus, disperse, or behave in any manner withoutchanging the scope of this disclosure.

Additionally, the input signal 201 or the one or more output signals 219may pass through any portion of the components of the WSS 200. Forexample, the input signal 201 is not limited to pass through the middleof the optical subsystem 209. Rather the input signal 201 may passthrough the optical subsystem 209 near an edge of the optical subsystem209, sufficient to substantially disperse the input signal 209 intoseparate input channels 206 of the input signal 201. The input signal201 or the one or more output signals 219 may be configured to similarlypass through any portion of the components of the WSS 200, individuallyor in any combination, without changing the scope of the disclosure.

The optical subsystem 209 is illustrated in FIGS. 2a-2d as includingboth the collimating lens 211 and the dispersive element 213 as discretecomponents, with the cylindrical lens 215 being a discrete componentwith respect to the optical subsystem 209. In other embodiments, two ormore of the collimating lens 211, the dispersive element 213, and thecylindrical lens 215, or at least their respective functionality, may beintegrated into a single component. For example, one or both of acollimating lens and a cylindrical lens (or associated structure) may beincorporated into the structure of a dispersive element such as adiffraction grating, similar in at least some respects to a Fresnellens.

Furthermore, it is well known in the art that in general opticalsystems, lenses may be replaced with other elements such as shapedmirrors to produce substantially similar results. As such, the lensesmentioned in the present disclosure are not limited to elements in whichlight passes through, but may be replaced by any number and combinationof shaped mirrors that produce substantially similar results of theaforementioned lenses described in the disclosure.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the presentdisclosure and the concepts contributed by the inventor to furtheringthe art, and are to be construed as being without limitation to suchspecifically recited examples and conditions. Although embodiments ofthe present disclosure have been described in detail, it should beunderstood that the various changes, substitutions, and alterationscould be made hereto without departing from the spirit and scope of thepresent disclosure.

The invention claimed is:
 1. A wavelength selective switch, comprising:a steering element; an optical subsystem configured to collimate anddemultiplex an input multimode optical signal into input discretewavelength channels, the optical subsystem comprising a collimating lensand a dispersive element, wherein: the optical subsystem is locatedbetween a fiber array and the steering element; and the collimating lensis located between the fiber array and the dispersive element; acylindrical lens located between the optical subsystem and the steeringelement.
 2. The wavelength selective switch of claim 1, wherein: thecollimating lens is positioned substantially one collimating lens focallength from the fiber array; the steering element is positionedsubstantially one collimating lens focal length from the collimatinglens; the cylindrical lens is positioned substantially one cylindricallens focal length from the steering element; and the cylindrical lens ispositioned substantially one cylindrical lens focal length from thedispersive element.
 3. The wavelength selective switch of claim 1,wherein the collimating lens comprises an aspheric lens.
 4. Thewavelength selective switch of claim 1, wherein the dispersive elementcomprises a diffraction grating.
 5. The wavelength selective switch ofclaim 1, wherein the steering element comprises a liquid crystal onsilicon device.
 6. The wavelength selective switch of claim 1, whereinthe fiber array comprises an array of multimode fibers.
 7. Thewavelength selective switch of claim 1, wherein: the optical subsystemis configured to collimate and demultiplex the input multimode opticalsignal into input discrete wavelength channels, wherein the opticalsubsystem is configured to receive the input multimode optical signalfrom an input fiber of the fiber array that includes the input fiber anda plurality of output fibers; the cylindrical lens is configured tofocus in one dimension the input discrete wavelength channels onto thesteering element; and the steering element is configured toindependently redirect the input discrete wavelength channels, such thatthe redirected input discrete wavelength channels become output discretewavelength channels; wherein: the cylindrical lens is further configuredto diverge in one-direction the output discrete wavelength channels ontothe optical subsystem; and the optical subsystem is further configuredto converge the output discrete wavelength channels onto at least oneoutput fiber of the plurality of output fibers.
 8. A wavelengthselective switch comprising: an optical subsystem configured tocollimate and demultiplex an input multimode optical signal into inputdiscrete wavelength channels, wherein the optical subsystem isconfigured to receive the input multimode optical signal from an inputfiber of a fiber array that includes the input fiber and a plurality ofoutput fibers; a cylindrical lens configured to focus in one dimensionthe input discrete wavelength channels onto a steering element, whereinthe cylindrical lens is positioned to be substantially one focal lengthof the cylindrical lens from the optical subsystem and substantially onefocal length of the cylindrical lens from the steering element; and thesteering element configured to independently redirect the input discretewavelength channels, such that the redirected input discrete wavelengthchannels become output discrete wavelength channels; wherein: thecylindrical lens is further configured to diverge in one-direction theoutput discrete wavelength channels onto the optical subsystem; and theoptical subsystem is further configured to converge the output discretewavelength channels onto at least one output fiber of the plurality ofoutput fibers.
 9. The wavelength selective switch of claim 8, whereinthe optical subsystem comprises: an aspheric lens configured tocollimate the input multimode optical signal, wherein the aspheric lensis positioned such that there is substantially one focal length of theaspheric lens between the aspheric lens and the fiber array and there issubstantially one focal length of the aspheric lens from the asphericlens to the steering element; and a dispersive element configured todemultiplex the collimated input multimode optical signal, wherein theaspheric lens is further configured to converge the output discretewavelength channels onto at least one output fiber.
 10. The wavelengthselective switch of claim 9, wherein: fibers of the fiber array arevertically spaced apart from each other in a line; the dispersiveelement is configured to demultiplex the collimated input multimodeoptical signal by being angled relative to the input fiber tohorizontally separate the input discrete wavelength channels within thecollimated input multimode optical signal from each other; and thesteering element is configured to independently redirect the inputdiscrete wavelength channels by independently vertically redirecting theinput discrete wavelength channels.
 11. The wavelength selective switchof claim 9, wherein the dispersive element comprises a diffractiongrating.
 12. The wavelength selective switch of claim 8, wherein thesteering element comprises a liquid crystal on silicon device.
 13. Amethod comprising: collimating an input multiplexed multimode opticalsignal; demultiplexing the input multiplexed multimode optical signalinto discrete wavelength channels; focusing each of the discretewavelength channels in one dimension, such that the discrete wavelengthchannels are incident on a steering element in substantially differentlocations; selectively redirecting the discrete wavelength channels;collimating the redirected discrete wavelength channels in the onedimension; and converging each of the redirected discrete wavelengthchannels into at least one output fiber.
 14. The method of claim 13,wherein converging each of the redirected discrete wavelength channelsinto the at least one output fiber comprises converging each of theredirected discrete wavelength channels into a different correspondingone of a plurality of output fibers.
 15. The method of claim 13, whereinconverging each of the redirected discrete wavelength channels into theat least one output fiber comprises converging all of the redirecteddiscrete wavelength channels into a single output fiber.
 16. The methodof claim 13, wherein: demultiplexing the input multiplexed multimodeoptical signal into discrete wavelength channels includes horizontallyseparating, at least partially, the discrete wavelength channels fromeach other; focusing each of the discrete wavelength channels in onedimension comprises focusing each of the discrete wavelength channelshorizontally; and collimating the redirected discrete wavelengthchannels comprises horizontally collimating the redirected discretewavelength channels.
 17. The method of claim 16, wherein thehorizontally separating occurs in response to dispersing the discretewavelength channels by a dispersive element.